1. Field of the Invention
The invention relates to an implantable arrangement for mechanical coupling of an output driver part of an active or passive hearing system to a preselected coupling site on the ossicular chain, the footplate of the stapes or a membrane which closes the round window or an artificial window in the cochlea, in the vestibulum or in the labyrinth (equilibrium organ), via a coupling arrangement which has a coupling element which can be connected, preferably by force-fit, to a preselected coupling site, the driver part being adapted to be excited to mechanical vibrations.
2. Description of Related Art
Partially implantable or fully implantable hearing systems for direct mechanical stimulation are known. In these hearing systems, the acoustic signal is converted into an electrical signal with a converter (microphone) and is amplified in an electronic signal processing stage, this amplified electrical signal is supplied to an implanted electromechanical converter with output-side mechanical vibrations which are supplied directly, i.e., with direct mechanical contact, to the middle ear or inner ear. This applies regardless of whether pure labyrinthine deafness with a completely intact middle ear or combined deafness (middle ear and inner ear damaged) is to be rehabilitated. Therefore, implantable electromechanical converters and processes for direct coupling of the mechanical converter vibrations to the intact middle ear or to the inner ear, respectively, for rehabilitation of pure labyrinthine deafness and also to the remaining ossicles of the middle ear in an artificially or pathologically altered middle ear for treatment of conductive deafness and their combinations have been described in the more recent scientific and patent literature.
Basically, all physical conversion principles can be used as electromechanical converter processes, such as electromagnetic, electrodynamic, magnetostrictive, dielectric, and piezoelectric. In recent years, various research groups have focused essentially on two of these processes: electromagnetic and piezoelectric. An outline of these converter versions can be found in Zenner and Leysieffer (HNO 1997 Vol. 45, 749-774).
In the piezoelectric process, mechanically direct coupling of the output-side converter vibrations to the middle ear ossicle or directly to the oval window is necessary. In the electromagnetic principle the force coupling, on the hand, can take place via an air gap (xe2x80x9ccontactlessxe2x80x9d), i.e., only one permanent magnet is placed by permanent fixation in direct mechanical contact with a middle ear ossicle. On the other hand, it is possible to dispose the entire converter within a housing (the coil and the magnet being coupled with the smallest possible air gap) and to transfer the output-side vibrations via a mechanically stiff coupling element with direct contact to the middle ear ossicle (Leysieffer et al. 1997 (HNO 1997, Vol. 45, pp. 792-800).
The patent literature contains some of the aforementioned versions of both electromagnetic and also piezoelectric hearing aid converters: U.S. Pat. Nos. 5,707,338 (Adams et al.), 5,554,096 (Ball), 3,712,962 (Epley), 3,870,832 (Fredrickson), 5,277,694 (Leysieffer et al.), 5,015,224 (Maniglia), 3,882,285 (Nunley), and 4,850,962 (Schaefer), International Patent Application publication Nos. WO 98/06235 (Adams et al.), WO 98/06238 (Adams et al.), WO 98/06236 (Kroll et al.) and WO 98/06237 (Bushek et al.), and published European Patent Application Nos. EP-A-0 984 663 (corresponding to commonly owned, U.S. Application Ser. No. 09/275,872) (Leysieffer), and EP-A-0 984 665 (corresponding to commonly owned U.S. Application Ser. No. 09/311,563) (Leysieffer).
The partially implantable piezoelectric hearing system of the Japanese group of Suzuki and Yanigahara presupposes, for implantation of the converter, the absence of the middle ear ossicles and an empty tympanic cavity in order to be able to couple the piezoelement to the stapes (Yanigahara et al.: Efficacy of the partially implantable middle ear in middle and inner ear disorders. Adv. Audiol, Vol. 4, Karger Basel (1998), pp. 149-159; Suzuki et al.: Implantation of partially implantable middle ear implant and the indication. Adv. Audiol., Vol. 4, Karger Basel (1988), pp. 160-166). Similarly, in the process of a partially implantable hearing system for those suffering from labyrinthine deafness according to U.S. Pat. No. 4,850,962 (Schaefer), basically, the incus is removed in order to be able to couple a piezoelectric converter element to the stapes. This also applies especially to other developments which are based on Schaefer technology and which are documented in the aforementioned disclosures (U.S. Pat. No. 5,707,338, and International Patent Application publication Nos. WO 98/06235, WO 98/06238, WO 98/06236, WO 98/06237).
Conversely, the electromagnetic converter of BALL (xe2x80x9cFloating Mass Transducer FMT,xe2x80x9d U.S. Pat. Nos. 5,624,376 and 5,554,096) is fixed with titanium clips directly on the long process of the incus when the middle ear is intact. The electromagnetic converter of the partially implantable system of FREDRICKSON (Fredrickson et al.: Ongoing investigations into an implantable electromagnetic hearing aid for moderate to sever sensorineural hearing loss. Otolaryngologic Clinics of North America, Vol. 28/1 (1995), pp. 107-121) is mechanically coupled directly to the body of the incus when the ossicular chain of the middle ear is likewise intact. The same applies to the piezoelectric and electromagnetic converters of LEYSIEFFER (Leysieffer et al.: An implantable piezoelectric hearing aid converter for patients with labyrinthine deafness. HNO 1997/45, pp. 792-800, U.S. Pat. No. 5,277,694, and published European Patent Application Nos. EP-A-0 984 663 and EP-A-0 984 665). Also, in the electromagnetic converter system of MANIGLIA (Maniglia et al: Contactless semi-implantable electromagnetic middle ear device for the treatment of sensorineural hearing loss, Otolaryngologic Clinics of North America, Vol. 28/1 (1995) pp. 121-141), when the ossicular chain is intact, a permanent magnet is permanently fixed mechanically to the ossicular chain but is, however, mechanically driven via an air gap coupling by a coil.
In the described converter and coupling versions, basically, two implantation principles can be distinguished:
a) In the case of the one principle the electromechanical converter with its active converter element is located itself in the middle ear region in the tympanic cavity and the converter is directly connected there to an ossicle or the inner ear (U.S. Pat. Nos. 4,850,962, 5,015,225, 5,707,338, 5,624,376, 5,554,096, and International Patent Application publication Nos. WO 98/06235, WO 98/06238, WO 98/06236, and WO 98/06237).
b) In the other principle the electromagnetic converter with its active converter element is located outside of the middle ear region in an artificially formed mastoid cavity, the output-side mechanical vibrations are then transmitted to the middle or inner ear by means of mechanically passive coupling elements via suitable surgical accesses (the natural aditus ad antrum, opening of the chorda-facialis angle or via an artificial hole from the mastoid) (Fredrickson et al.: Ongoing investigations into an implantable electromagnetic hearing aid for moderate to severe sensorineural hearing loss. Otolaryngologic Clinic of North America, Vol. 28/1 (1995), pp. 107-121: U.S. Pat. No. 5,277,694; published European Application Nos. EP-A-0 984 663, EP-A-0 984 665).
In a) type versions, the converter can be made as a so-called xe2x80x9cfloating massxe2x80x9d converter, i.e., the converter element does not require any xe2x80x9creactionxe2x80x9d via secure screwing to the skull bone, but it vibrates based on the laws of mass inertia with its converter housing and transmits these vibrations directly to a middle ear ossicle (U.S. Pat. Nos. 5,624,376, 5,554,096, and 5,707,338, and International Patent Application publication no. WO 98/06236). On the one hand, this means that an implantable fixation system on the cranial vault can be advantageously omitted; on the other hand, this version disadvantageously means that bulky artificial elements must be placed in the tympanic cavity and their long-term stability and biostability are currently not known or guaranteed, especially in the case of temporary pathological changes of the middle ear (for example, otitis media). Another major disadvantage is that the converter together with its electrical supply line has to be transferred from the mastoid into the middle ear and must be fixed there using suitable surgical tools; this requires expanded access through the chorda facialis angle, and thus, entails a latent hazard to the facial nerve which is located in the immediate vicinity.
In the converter versions as per b), the converter housing with the implantable positioning and fixation systems is attached to the cranial vault (advantageous embodiment U.S. Pat. No. 5,788,711). Both in the partially implantable system in FREDRICKSON (Ongoing investigations into an implantable electromagnetic hearing aid for moderate to severe sensorineural hearing loss. Otolaryngologic Clinics of North America, Vo. 28/1 (1995), pp. 107-121) as well as in the fully implantable hearing system of LEYSIEFFER and ZENNER (HNO 1998, vol. 46, 853-863 and 844-852), when the vibrating driver part is coupled to the body of the incus, it is assumed for permanent and mechanically secure vibration transmission that the tip of the coupling rod which is placed in the laser-induced depression of the middle ear ossicle undergoes osseointegration over the long term, i.e., the coupling rod coalesces solidly with the ossicle and thus ensures reliable transmission of dynamic compression and tensile forces. However, this long-term effect is currently not yet scientifically proven or certain. Furthermore, in this type of coupling, in case of a technical converter defect, there is the disadvantage that decoupling from the ossicle to remove the converter can only be done with mechanically based surgical methods; this can mean considerable hazard to the middle ear and especially the inner ear.
The major advantage of these converter embodiments as per b), however, is that the middle ear remains largely free and coupling access to the middle ear can take place without major possible hazard to the facial nerve. One preferable surgical process for this purpose is described in U.S. Patent Application Ser. No. 09/168,079. Basic advantageous forms of passive coupling elements for transmission of the output-side converter vibrations from the mastoid to the middle ear or inner ear are described in U.S. Pat. Nos. 5,277,694 and 5,941,814 and in HNO 1998 Vol. 46, pp. 27-37 Lehner et al.: xe2x80x9cCold-flowing elements for coupling of an implantable hearing aid converter to the auditory ossicle or perilymph.xe2x80x9d The coupling elements are especially made of gold, preferably soft-annealed fine gold, in the form of a C-band for the long process of the incus, a band loop for the long process of the incus and a tiny bell for the head of the stapes, and these coupling elements can be coupled using instruments which are standard in ear surgery, and if necessary, they can also be detached again.
In both active and passive hearing systems, a large transmission bandwidth is desirable to be able to faithfully transmit music signals, for example, in addition to speech signals. In doing so, in addition to the spectral demands on the hearing system, the dynamic operating behavior also plays an important role when it is a matter or reproducing as faithfully as possible the time envelope curve behavior of an audio signal, especially for highly variable signal portions, such as plosives in speech discrimination and for pulse-containing portions in music transmission. Furthermore, for active hearing systems, frequency-independent mechanical deflection of the output driver part and of the coupling elements connected thereto at a constant voltage of the electromechanical converter generally is desirable. Known coupling elements in the vibration transmission path between the output driver part and the preselected coupling site, for example, in the form of metallic or ceramic coupling rods of an active hearing system or of prostheses produced from bio-ceramic materials in a passive hearing system, typically have a high resonance sharpness (high Q-factor): pronounced linear distorsions occur. A high mechanical quality can also occur on the side of the electromechanical converter. As a result, undesirable resonance phenomena can occur within the wide transmission range. This applies especially when the electromechanical converter is housed in the mastoid cavity, because in the relation of the size of the massive coupling element to the volume of the dynamic portions of the active converter element present in this case, a clear effect of the coupling element on the dynamic properties, and thus, on the entire transmission function of the converter system must be expected. It is known (International Patent Application publication WO 99/15111) that provisions can be made for attenuation in the transmission path between an active converter element of an active hearing system and a coupling site on the ossicular chain by inserting a flexible connection part, for example, in the form of a spring or a urethane strip, between the converter element and the coupling element which can be drivingly connected to the coupling site. The flexible connection part which sits between the coupling element and the active converter element provides for elastic coupling of the active converter element to the coupling element. It is furthermore known (Alaa El SEIFI: The Necrosed Incus in Stapedectomy Revision, Laryngoscope 106, April 1996, pp. 511-512) in cases in which a wire loop which has been provided for coupling a passive stapes prosthesis to an incus stump has become loose, to push a piece of hose made of Silastic(copyright) which is slit over part of its longitudinal dimension over the wire loop and the incus stump in order to press the wire loop in this way against the incus stump and to restore coupling between the two.
The object of this invention is to devise an implantable arrangement for mechanical coupling of an output driver part of an active or passive hearing system, the driver part being adapted to be excited to mechanical vibrations, and said arrangement having advantageous properties for transmission of vibrations from the output driver part to a preselected coupling site on the ossicular chain, the footplate of the stapes or a membrane which closes the round window or an artificial window in the cochlea, in the vestibulum or in the labyrinth (equilibrium organ), which arrangement promotes an optimum form of vibration of the footplate of the stapes or the aforementioned membrane and keeps the risk of damage to the natural structures in the region of the coupling site during and after implantation especially low.
Starting from a device of the type having an implantable arrangement for mechanical coupling of an output driver part of an active or passive hearing system, the driver part being excitable to mechanical vibrations, to a preselected coupling site on the ossicular chain, the footplate of the stapes or a membrane which closes the round window or an artificial window in the cochlea, in the vestibulum or in the labyrinth (equilibrium organ), via a coupling arrangement which has a coupling element which can be connected to a preselected coupling site, this object is achieved in accordance with the invention by the provision of an attenuator having entropy-elastic properties and, in the implanted state, resting against the coupling site.
An attenuator with entropy-elastic properties is defined here as an attenuator which has at least a certain entropic elasticity, optionally in combination with energy or steel elasticity (see in the regard DIN 7724). Entropic elasticity (also called rubber elasticity) means that elastic deformation proceeds essentially without a change of the internal energy. Entropic elasticity is due to the effort of large macromolecules to assume a form as random as possible.
The arrangement according to the invention provides in an especially simple, and at the same time, reliable manner for achieving a relatively flat frequency response for the deflection which occur at the preselected coupling site as a function of the vibrations of the output-side driver part. Another important advantage is that the coupling site, for example, of the ossicle is not xe2x80x9crestrainedxe2x80x9d mainly in the direction of vibration of the driving converter, since such xe2x80x9crestraintxe2x80x9d can lead to a less than optimum form of vibration of the footplate of the stapes in the oval window. (One preferable form of vibration is a piston-like vibration of the footplate of the stapes perpendicular to its plane). Rather, the ossicle, as a result of the non-rigidity or pliability of the attenuator, sets itself (frequency-dependent) direction of vibration based on the dynamic properties of the intact middle ear. This advantage also applies to a non-intact, (partially) decomposed ossicular chain and coupling to the xe2x80x9cremainderxe2x80x9d of the chain facing the inner ear, and in the extreme case, also to only a residual stapes or only the footplate of the stapes since it is suspended by the so-called ligament (the elastic annular ligament which xe2x80x9choldsxe2x80x9d the stapes in the oval window). Moreover the attenuator effectively protects the coupling site against damage by the coupling element both during and also after implantation.
In another embodiment of the invention, the attenuator in the implanted state can be positioned at least partially between the coupling element and the coupling site. In doing so, the attenuator can be advantageously made as a molded part which in the implanted state at least partially surrounds part of the ossicular chain. As attenuator, however, there can also be provided a coating with entropy-elastic properties on the side of the coupling element which comes into contact with the coupling side.
According to a modified embodiment of the invention, the vibration transmission path has a coupling rod which is drivingly connected to the output driver part and a coupling element which can be drivingly connected to the preselected coupling site and which is attached to the coupling rod, the attenuator being made as a coating with entropy-elastic properties, which at least partially surrounds the coupling element, wherein in the implanted state, part of the coating is disposed between the coupling element and the coupling site.
In another modified embodiment of the invention, the vibration transmission path has a coupling rod which is drivingly connected to the output driver part and a coupling element which can be drivingly connected to the preselected coupling site and which is connected to the coupling rod, and the attenuator sits between the coupling rod and the coupling element. In doing so, it is practical for the attenuator to be located between the coupling rod and the coupling element. In particular, as the attenuator, an essentially cylindrical molding can be used which is provided with receivers for the coupling element-side end of the coupling rod and for the coupling rod-side end of the coupling element. But, this can also be done such that the coupling rod-side end of the coupling element surrounds the coupling element-side end of the coupling rod with the formation of a gap between these two ends and the gap is at least partially filled with a material which forms the attenuator with entropic elastic properties.
According to another embodiment of the invention, the coupling element itself is made as the attenuator. Thus, as the coupling element and the attenuator, a free end of a molded part with entropy-elastic properties can be inserted into the space between the stapes and the footplate of the stapes.
Especially cross-linked silicones or another implantable rubber-like material are suitable as the material for the attenuator.
The arrangement in accordance with the invention can be part of an active hearing system in which the output driver part is a vibratory part, especially a vibratory membrane, of an electromechanical hearing aid converter. The arrangement of the invention can, however, also be part of a passive hearing system, especially a partial or full middle ear prosthesis in which in the implanted state the eardrum is used as the output-side driver part.
Preferred embodiments of the arrangement in accordance with the invention are explained in detail below using the attached drawings.